Calpurnia takes Jem and Scout to her church in Chapter Twelve of To Kill a Mockingbird. The night before the service, Calpurnia bathes both Jem and Scout, and she reviews their clothing (a suit for Jem and a dress with petticoats and a pink sash for Scout) and treats the material with starch the morning of. Jem wryly comments that with all this fuss, "It's like we were goin' to Mardi Gras."
The church that Calpurnia takes them to is First Purchase African M.E. Church in the Quarters; the building was purchased with the first earnings of freed slaves and contains the only steeple and bell in all of Maycomb.
When the trio first arrives at the church, the men take off their hats and the women cross their arms, which Scout describes as "weekday gestures of respectful attention." One woman, Lula, is not amused that Calpurnia has brought white children to a black church. Jem and Scout want to leave to avoid causing trouble, but another church member, Zeebo, assures them that they are welcome there.
Scout and Jem are surprised at the lack of decor, hymn-books, or traditional instruments for church music. Despite these superficial differences, the sermon is much the same as the one given at their own church... with the exception of the calling out of individuals who have sinned in some capacity. The service closes with continued money-collecting on the behalf of Helen Robinson, who cannot find work due to people's skepticism about her as the wife of Tom Robinson.
This experience is significant because, as Scout puts it, the children discover "[t]hat Calpurnia led a modest double life... a separate existence outside our household... having command of two languages." This recognition of Calpurnia's private life and multidimensional existence as a human being is critical; she is no longer viewed by Scout as merely the black woman who works in the Finch household. She is a person beyond her housekeeping and the color of her skin, one with very real desires, needs, principles, cultural values, etc.